Ch 7Cell Cycle — Class 11 Botany, concept-first.

Among the defining abilities of a living cell is its capacity to grow and divide. Every new cell traces its origin to an already-existing cell that has split in two, cells are never created from scrat…

The idea that cells divide to produce new cells was built up over more than two centuries of observation, from Robert Hooke's first use of the word 'cell' in 1665 to the identification of chromosomes…

The nucleus is the organising centre of the cell because it houses the chromosomes, the structures that carry the cell's hereditary information.

Chromosomes are only visible as distinct, condensed, multicoiled bodies at the time the nucleus divides; for most of the cell's life the same genetic material exists as long, thin, uncoiled threads th…

There are two kinds of nuclear division. In mitosis, the daughter cells end up with exactly the same chromosome number as the parent cell - typically the diploid (2n) number - so mitosis is described…

The cell cycle is defined as the series of events that leads to the formation of a new cell from an existing one; the phenomenal changes that build up a new cell population all occur within this cycle…

The duration of the cell cycle, and of each phase within it, differs between cell types and organisms - some embryonic cells complete a cycle in under an hour, while some specialised adult cells may t…

Interphase is the longest part of the cell cycle but its length is extremely variable between cell types.

G1 is the first gap phase of the cell cycle, occurring immediately after a cell has finished dividing. At this point the cell's DNA content is at its unreplicated 2C level.

Some cells leave G1 and enter a non-dividing, quiescent stage called G0, where they remain metabolically active but do not proliferate; a cell can stay in G0 for a very long time, and while there it t…

S phase, the synthesis phase, is the stage of interphase during which the cell's DNA is actually replicated; cells caught in S phase therefore show an intermediate DNA content, somewhere between the 2…

G2 is the second gap phase, occurring after DNA replication is complete; the DNA content stays at the replicated 4C level throughout G2 and into mitosis, since no further copying occurs.

Cell division is the process by which one parent cell gives rise to two (or, in meiosis, four) daughter cells, and it is the mechanical culmination of everything the cell cycle has been building towar…

Amitosis, also called direct or incipient cell division, is the simplest of the three patterns of cell division.

Mitosis concerns the events that take place inside the nucleus during division, and it is the most extensively studied form of nuclear division because it is by far the most common.

Mitosis can proceed in two structurally different ways depending on what happens to the nuclear envelope.

Cytokinesis is the division of the cytoplasm that normally follows karyokinesis and completes the formation of two separate daughter cells; in many cells cytokinesis actually begins during telophase,…

Mitosis produces an exact copy of the parent cell, genetically identical in every respect, and this single property underlies all of its biological uses.

Meiosis takes its name from the Greek meioum, meaning to reduce, and it is unique among the forms of nuclear division for three linked reasons: it involves synapsis (the pairing of homologous chromoso…

Meiosis serves three closely related biological purposes. First, it maintains a constant, definite chromosome number across generations of a sexually reproducing species: because meiosis halves the ch…

Comparing mitosis and meiosis side by side makes their very different biological roles clear. Structurally, plant and animal mitosis themselves already differ in some details: animal cells possess cen…

Mitogens are the factors that promote proliferation through the cell cycle - substances that push a resting or slowly cycling cell towards, and through, another round of division.

The Evaluation exercise brings together the whole chapter: the first ten items are single-best-answer MCQs testing recall and application of cell-cycle sequencing, checkpoint terminology (G0, restrict…

Sample papers and previous-year board questions for this subject.